Cardiac surgery−related acute kidney injury (AKI) is a common postoperative complication that greatly increases morbidity and mortality. There are currently no effective interventions to prevent AKI associated with cardiac surgery. Experimental data have shown that administration of the mineralocorticoid receptor blocker spironolactone prevents renal injury induced by ischemia-reperfusion in rats. The objective of this study was to test whether short-term perioperative administration of oral spironolactone could reduce the incidence of AKI in cardiac surgical patients.